Psoriasis causes patches of scaly, red, or white skin called plaques. Psoriatic arthritis sets off joint swelling and pain that can lead to permanent damage. Your immune system is responsible for both.
An accurate and early diagnosis of psoriatic arthritis will help you avoid the damage and deformity it can cause.
Your doctor will make a decision based on:
A physical exam
Your medical history and your family's
No single thing will diagnose psoriatic arthritis, but blood tests, imaging, and other tests can help your doctor. He may want to give you certain tests that check for rheumatoid arthritis, because it can look a lot like psoriatic arthritis.
Inflammation is part of both psoriasis and psoriatic arthritis. It's a sign your immune system is working. But both of these conditions happen because your immune system attacks your body instead of something from outside.
About a third of people who have psoriasis will get psoriatic arthritis. Doctors can't yet tell who before it happens, though.
Usually, you'll have the skin symptoms first. But sometimes, arthritis symptoms appear months, or even years, before skin problems do. That makes it hard to diagnose.
People with severe psoriasis could have a greater chance of getting psoriatic arthritis.
Psoriasis skin plaques can flare up and then get better. Psoriatic arthritis symptoms may also come and go.
About 40% of people who get psoriatic arthritis have relatives with it or with psoriasis. Scientists don't know which genes are responsible for these conditions. Figuring that out will help doctors predict who is likely to get these conditions. It may lead to new treatments, too.
How They're Different
There's no connection between the location of your plaques and which joints are affected. For example, you could have:
Skin lesions on your elbow, but no pain, no swelling, and no problems bending and moving it
Swollen toes, but no redness or scales on your feet
Psoriasis doesn't cause scarring or any other lasting harm to skin. But psoriatic arthritis can damage joints and leave them stiff and deformed if it isn't treated.
That's why you need to work with your doctor even if your symptoms get better. Don't stop taking medications unless your doctor says it's OK.